Pulse-echo distance indicator



w. D. HERSHBERGER PULSE-ECHO DISTANCE INDICATOR Filed Jan. 5o, 194s n Nm Bmnentor Cttorneg "VVVVV July 9, i946.

Patented July 9, 1946 PULSE-ECHO DISTANCE INDICATOR William D. Hershberger, Princeton, N. J., assignor to Radio Corporation of America, a corporation o! Delaware Application January so, 1943, serial No. 474,159

(ci. 25o-1) 7 Claims. l

My invention relates to pulse-echo systems for indicating the presence of or the distance to reflecting objects.

The invention will be described as applied to radio locator apparatus which transmits short periodically recurring radio pulses and which receives these pulses after they are reflected from a reflecting object or surface. It is well known that the distance to the reflecting object or surface can be determined by measuring the time interval that has elapsed between the transmission of a pulse and the reception of the reflected pulse. This time interval is commonly measured by means of a cathode ray indicator tube.

An object of the present invention is to provide in a pulse-echo system a method of and means for producing an indication when the distance to a reecting object or surface falls outside of predetermined distance limits.

A further object of the invention is to provide an improved indicator for a radio altimeter of the pulse-echo type.

A still further object of the invention is to provide an improved distance indicator for a pulse-echo system.

In one preferred embodiment of the invention a radio altimeter is provided with two indicating devices (two lamps, for example) which are connected to receive the reflected pulses from two amplifiers, respectively, under certain conditions. These amplifiers are normally biased to cut-ofi but are rendered operative periodically at such intervals that the lamps are lighted only when the altitude is less than a predetermined altitude limit or when the altitude or the distance to a reflecting surface is greater than a predetermined altitude or distance limit and within the range of the altimeter. The latter condition is encountered either when the aircraft exceeds a predetermined altitude or when there is an obstage such as a mountain in the path of the aircra The above-mentioned periodic biasing or keying of the amplifiers may be accomplished by applying positive rectangular voltages thereto from trigger amplifiers or multivibrators. The output from one trigger amplifier renders the amplifier for one lamp operative for a short period immediately following the transmission of a pulse while the output from the other trigger am.. plier renders the amplifier for the other lamp operative for a short period immediately preceding the transmission oi a pulse. Between these two periods the reception of a reflected pulse will not light either one of the indicator lamps.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Figure 1 is a block diagram of one embodiment of the invention; Figure 2 is a group of graphs which are referred to in explaining the invention; and Figure 3 is a circuit diagram of a phase shifter that may be employed in the apparatus of Fig. 1. In the several figures similar parts are indicated by similar reference characters.

In Fig. 1 the invention is shown applied to a radio altimeter which comprises a sine wave oscillator I0, a wave shaper I I for producing periodic pulses 5, and a keyer I 2 for modulating or keying a high frequency radio transmitter I3 by the pulses 5 whereby pulses of radio frequency energy are radiated to the reflecting object or surface. In the case of an altimeter mounted on an aircraftto give an indication of an obstacle ahead as well as an indication of altitude, the radiation of the pulses is downward and forward.

The reflected pulses are received and demodulated by a receiver I6. The resulting pulses, indicated at I1, are supplied to an amplifier Ii! which is connected to energize an indicator lamp I9, and to an amplifier 2| which is connected to energize an indicator lamp 22. The amplifiers I8 and 2| are normally biased to cut-off so that the received pulses I 1 will not energize the indicator lamps I9 and 22 unless the positive pulses 23 and 24 are being impressed upon the amplifiers I 8 and 2 I, respectively. Negative pulses 5' may be supplied to the receiver I6 over a conductor 20 to make it insensitive during the transmission of a pulse.

Referring to Fig. 2, the positive rectangular pulses '23 are initiated by the transmitter keying pulses 5 and last for an adjustable period following the transmitted pulse. The positive rectangular pulses 24 are initiated at an adjustable time after the termination of the pulses 23 and last until the occurrence of the next transmitter keying pulse 5. It will be apparent that if the reected pulses arrive at the receiver at a time between the end of a pulse 23 and the start of a pulse 24, neither of the indicator lamps I9 and 22 will be lighted. If' lamp I9 lights, it indicates that the aircraft is too low; if lamp 22 lights, it indicates either that the aircraft is too high or that there is an obstacle ahead.

The rectangular pulses 23 and 24 may be obtained by supplying signal from the sine wave oscillator I0 to the adjustable phase Shifters 3| and 32 (one of which is shown in detail in Fig. 3). The sine wave signals from the phase shifters 3| and 32 are supplied to suitable wave shapers 33 and 34, respectively, to produce voltage pulses, indicated at 38 and 31, which have a repetition rate equal to the frequency of the sine wave signals. Suitable wave shapers are well known and may comprise, for example, a clipping tube or tubes for changing the sine waves to waves that are substantially rectangular, a diiferentiating circuitl for obtaining narrow pulses from the substantially rectangular waves, and additional clipping means.

The pulses 36 and 31 are impressed upon trigger amplifiers or multlvibrators 38 and 38, respectively, at the proper .points so that pulse 36 terminates the rectangular pulse 23 produced by trigger ampliiler 38, and so that pulse 31 initiates the rectangular pulse 24 produced by trigger ampliiler 38. The time relation between the several pulses is shown in Fig. 2. The start of the pulse 23 and the termination oi' the pulse 24 are determined by the keying pulse which may be supplied from the wave shaper Il over a conductor 4| to the trigger ampliers 38 and 39. The time relations between the pulses 23 and 24 and the pulse 5 are shown in Fig. 2.

The phase Shifters 3| and 32 may be of the type shown in Fig. 3 in which inductance coils/46 and 4"l are placed so the axis of coil 48 makes an angle of 90 degrees with the axis of coil 41 and have signals applied to them 90 degrees out of phase to produce a. rotating iield. The 90 degree phase shift may be obtained by means of a resistor-capacitor network comprising resistors 5| and 52 and capacitor53. A rotatably adjustable pickup coil 48 is mounted in the rotating field whereby the desired phase relation of input signal to output signal may be obtained by turning a phase adjustment knob 3i'.

It will be apparent that the time of occurrence of the pulses 3B and 31 may be advanced or retarded by changing the adjustments of the phase Shifters 3| and 32, respectively. Thus, as indicated by the dotted line portions of the graphs in Fig. 2, the duration of the pulse 23 may be increased or decreased to determine the lower altitude limit at which the indicator lamp i9 will light, and the starting time of the pulse 24 may be changed to determine the upper altitude or distance limit at which the indicator lamp 22 will light. Therefore, as previously stated, one indicator will give a warning signal when the altitude of the aircraft is below a predetermined adjustable limit and the other indicator will give a warning when the altitude is above a predetermined adjustable limit or when an obstacle is being approached.

'I'he phase Shifters 3| and 32 preferably are calibrated in distance so that the distance to the reecting surface may be found by rotating the phase adjustment knobs 3 I or 32', respectively, to the point where the indicator lamps I9 or 22, respectively, either light up if previously dark or extinguish if previously lighted. For example, the altitude may be determined by adjusting the phase shifter 3| until the lamp i9 blinks on and oil when the knob 3| is rotated left and right very slight amounts. The pointer on knob 3|' theln shows the altitude reading on the associated sca e 6.

Similarly the altitude may be determined by adjusting the phase shifter 32 and reading the distance on' the scale 1. It may be noted that if, when in llight, the lamp 22 lights. the pilot cannot tell from this alone whether he has exceeded the upper limit of altitude or is approach- This can be checked quickly. l

ing an obstacle. however, by adjusting the phase shifter 3l to see what the altitude actually is, and, if necessary, by also adjusting the phase shifter 32 to ilnd the distance to the reflecting surface that has caused the lamp 22 to light.

I claim as my invention:

l. A pulse-echo system comprising means i'or transmitting pulses, means for receiving said pulses after reilection from a surface nr object, a pair of indicating devices, means for supplying the received pulses to said indicating devices. means for producing two groups oi' control pulses having a deilnite phase relation with respect to the transmitted pulses, and means responsive to said two groups of control pulses for making said indicating devices eiective, respectively, to produce an indication only during a predetermined period following the transmission of a pulse and an indication only during a predetermined period preceding the transmission of a pulse.

2. The invention according to claim 1 wherein means is provided for adjusting the widths of the control pulses in said two groups.

3. A pulse-echo system comprising means for transmitting periodically recurring pulses, means for receiving said pulses after reilection from a surface or object, an indicating device, means including an amplifier for supplying the received pulses to said indicating device, said amplifier normally being biased to cut-ofi', means for producing control pulses of positive polarity having a deiinite phase relation with respect to the transmitted pulses. means for adjusting the duration of said control pulses, and means for applying said positive control pulses to said amplifier to make it eilective to pass the received pulses to said indicating device for the duration of each control pulse. f

4. A pulse-echo system comprising means for transmitting perodically recurring pulses, means for receiving said pulses after reection from a surface or object, an indicating device, means including an amplifier for supplying the received pulses to said indicating device, said ampliiler normally being biased to cut-olf, means for producing control pulses having a known phase relation with respect to the transmitted pulses. means for adjusting the phase of said control pulses with respect to the transmitted pulses, means for producing positive control pulses having a duration which is determined by the phasing oi said control pulses, and means for applying said positive control pulses to said amplitler to make it effective to pass the received pulses to said indicating device for the duration of each control pulse.

5. A pulse-echo system comprising means for transmitting pulses, means for receiving said pulses after reflection from a surface or object, a pair of indicating devices, means including a pair of ampliers for supplying the received pulses to said pair of indicating devices, respectively, said ampliers normally being biased to 'cut-ofi. means for producing two groups oi.' control pulses of positive polarity having a known phase relation and duration with respect to the transmitted pulses, means for adiusting the duration of said control pulses with respect to the transmitted pulses, and means for applying said two groups of positive control pulses to said ampliners. respectively, to make them eiective to pass the received pulses to said indicating deviles for the duration ot each applied control p se.

6. A pulse receiver for a system that includes means for transmitting pulses. said receiver comprising means for receiving said transmitted pulses after they have been reilected from a surface or object, indicating means, means for supplying the received pulses to said indicating means, means for producing irst control pulses that occur immediately following the transmission of a pulse, means for producing second control pulses that occur immediately preceding the transmission of a pulse but after the termination oi the ilrst control pulses, and means responsive to said first and second control pulses for causing said indicating means to indicate whenl 6 prising means for receiving said transmitted pulses after they have been reected from a surface or object, two indicating devices; means for supplying the received pulses to said indicating devices, means for producing control pulses that occur immediately following the transmission of a pulse, means for producing second control pulses that occur immediately preceding the transmission of a pulse but after the termination oi the iirst control pulses whereby there is a certain period between a iirst control pulse and the following second control pulse, means responsive to said iirst control pulses for causing one of said indicating devices'to indicate when the reflected pulses are received during the occurrence of the iirst control pulses, and means responsive to said second control pulses for causing the other of said indicating devices to indicate when the reflected pulses are received during the D. HERSHBERGER.

Disclaimer 2,403,527.-Wl1'am D. Hershberger INDICATOR. Patent dated uly 9,

Princeton, N.

J. PULSE-Echo Drs'rsNcr:y 1946. Disclaimer filed Nov. 5, 1949,

by the assignee, Radio Corporation 0j America. Hereb enters this disclaimer to claims 3 and 4 of said patent.

[ Gazette DecemberI 27, 1949.] 

